1. Field of the Invention
The present invention relates to an oil seal for sealing out a sealing fluid such as oil and fuel. It relates, for example, to an oil seal for a reciprocating shaft which uses two-part fluid, and in particular to an oil seal used in a high pressure pump for an in-cylinder direct injection device of an automobile gasoline engine.
2. Description of the Related Art
High pressure pumps for in-cylinder injection devices use a conventional oil seal as shown in Japanese patent application No. 2000-097826. This requires return piping to the fuel tank to avoid fuel pressure on the oil seal, considering the pressure proof of the oil seal.
Also, oil seals that take conventional pressure proof into consideration need a backup ring between a retaining member and flexible member as described, for example, in JP-A-10-141508.
The related art described above needs pressure-reducing return piping to the fuel tank to avoid fuel pressure on the oil seal. This presents problems such as increases in the number of parts, increased costs, and increased man-hours for pipe routing.
If an oil seal is used under high pressure without pressure-reducing return piping to the fuel tank such as the one described above, it needs a backup ring or the like. This makes the oil seal structure complex. Furthermore, since high pressure acts only on one side, a load is applied to the entire seal member, causing the retaining member to move.
In the light of the above problems with the related art, it is an object of the present invention to improve the durability of oil seals under high pressure. Another object thereof is to simplify the entire system in which a fuel pump is used.
To attain the above objects, according to the present invention, the shapes of the retaining member and flexible member has been changed from the conventional ones. Alternatively, the flexible member is prevented from swelling due to the sealed fluid either by using a swell-resistant material for the flexible member or by applying surface treatment to the flexible member. Besides, according to the present invention, a low-friction material is used for the sealing surface of the retaining member or the mating surface, or it subjects the flexible member or the mating member to friction-reducing surface treatment to reduce the frictional forces of the sealing surface or the mating surface therewith. Furthermore, according to the present invention, a constraint is provided on the periphery of the seal member to prevent the seal member from moving under pressure.